TiAl intermetallic compound-based alloys and methods for preparing same

a compound-based alloy and alloy technology, applied in the field oftial intermetallic compound-based alloys, can solve the problems of insufficient plastic ductility, difficult plastic working, and inability to meet the requirements of industrial production, so as to improve oxidation resistance, reduce oxidation resistance, and improve the effect of stabilizing the beta

Inactive Publication Date: 2000-04-18
MITSUBISHI HEAVY IND LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The primary function of Nb is to improve oxidation resistance, but Nb is somewhat effective in stabilizing the .beta. phase. If the Nb concentration is less than 6 atomic percent, the effect of its addition is not recognized. On the other hand, if the Nb concentration is greater than 10 atomic percent, a reduction in oxidation resistance results.
Cr has the function of stabilizing the .beta. phase. If the Cr concentration is less than 1.5 atomic percent, the effect of its addition is not recognized. On the other hand, if the Cr concentration is greater than 3.5 atomic percent, the proportion of coarse .beta. phase is increased, resulting in a reduction in plastic workability.

Problems solved by technology

However, dies which can be used at 1100.degree. C. or above on an industrial production level are not available in the present situation.
Thus, their plastic working is difficult as a matter of fact and has not been put to practical use until now.
The .gamma. and .alpha.2 phases are both intermetallic compound phases and do not have sufficient plastic ductility even in a high-temperature region.
Because of the above-described factors associated with material characteristics, TiAl intermetallic compound-based alloys of the prior art composition fail to sufficient plastic workability at 1100.degree. C. or below.
If it is tried to work them at 1100.degree. C. or below, the material tends to develop defects such as cracks and cavities.
Moreover, owing to the high deformation resistance of the material, the die becomes unable to retain its original shape and is hence deformed.
Furthermore, the oxidation resistance of alloys of the prior art composition is rapidly reduced above 800.degree. C.
est. However, the high-temperature strength of the aforesaid structure is
strength. Accordingly, it may be said that the prior art TiAl alloys cannot be used as a substitute for su
ellae. The latter has high hardness at high temperatures, but is brittle and liable to cleavage fr
acture. Thus, this structure is destroyed before exhibiting the strength inherently possessed thereby, and consequently has similarly low strength at high tempe
Furthermore, the oxidation resistance of alloys of the prior art composition is rapidly reduced above 800.degree. C.
Also from this point of view, their service temperature is restricted.
However, their high-temperature strength, creep resistance and oxidation resistance, which are characteristics required for use in turbine blades and turbine rotors, are still low as compared with superalloys.
Accordingly, these alloys as such cannot be used as substitutes for superalloys.
Thus, the prior art TiAl alloys are inferior to superalloys even when the creep resistance is expressed in terms of specific strength.
Thus, the prior art TiAl alloys are markedly inferior in oxidation resistance.

Method used

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  • TiAl intermetallic compound-based alloys and methods for preparing same
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  • TiAl intermetallic compound-based alloys and methods for preparing same

Examples

Experimental program
Comparison scheme
Effect test

examples 4-6

show the results obtained when an alloy having an Al concentration of 48 atomic percent and additionally containing 3 atomic percent Cr was tested in the as-cast state or after heat treatment at 1200.degree. C. or 1300.degree. C. In all cases, the maximum stress during compression test was 170 MPa or greater and the development of defects was observed. Moreover, the oxidation weight gain was 24.1 mg / cm.sup.2 or greater, indicating that its oxidation resistance was unsatisfactory.

examples 7-12

relate to an alloy in accordance with the present invention and show the results obtained when an alloy comprising 42 atomic percent Ti, 47 atomic percent Al, 9 atomic percent Nb and 2 atomic percent Cr was tested in the as-cast state or after heat treatment at 1100.degree. C., 1150.degree. C., 1200.degree. C., 1250.degree. C. or 1350.degree. C. After heat treatment at 1150.degree. C. or 1200.degree. C., the maximum stress was 140 MPa or less and no defects were developed. On the other hand, in the as-cast state and after heat treatment at 1100.degree. C., 1250.degree. C. or 1350.degree. C., the maximum stress was 170 MPa or greater and the development of defects was observed. The oxidation weight gain was 3.5 mg / cm.sup.2 or less, indicating that its oxidation resistance was markedly superior as compared with Examples 1-6.

examples 13-18

relate to an alloy in accordance with the present invention and show the results obtained when an alloy comprising 45 atomic percent Ti, 45 atomic percent Al, 8 atomic percent Nb and 2 atomic percent Cr was tested in the as-cast state or after heat treatment at 1100.degree. C., 1150.degree. C., 1200.degree. C., 1250.degree. C. or 1350.degree. C. After heat treatment at 1150.degree. C. or 1200.degree. C., the maximum stress was 120 MPa or less and no defects were developed. On the other hand, in the as-cast state and after heat treatment at 1100.degree. C., 1250.degree. C. or 1350.degree. C., the maximum stress was 160 MPa or greater and the development of defects was observed. The oxidation weight gain was 3.3 mg / cm.sup.2 or less, indicating that its oxidation resistance was markedly superior as compared with Examples 1-6.

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Abstract

PCT No. PCT/JP95/01349 Sec. 371 Date Mar. 26, 1996 Sec. 102(e) Date Mar. 26, 1996 PCT Filed Jul. 6, 1995 PCT Pub. No. WO96/12820 PCT Pub. Date May 2, 1996TiAl intermetallic compound-based alloys comprising Ti, Al, Nb and Cr and, if necessary, further comprising Ni and Co, which have excellent plastic workability, good resistance to oxidation at high temperatures, high strength or good creep resistance.

Description

DESCRIPTION1. Technical FieldFirst, this invention relates to TiAl intermetallic compound-based alloys having excellent plastic workability and good resistance to oxidation at high temperatures and hence suitable for use in power-generating gas turbines, aircraft engines and the like, as well as a method for preparing the same.Secondly, this invention relates to TiAl intermetallic compound-based alloys having high strength and good resistance to oxidation at high temperatures and hence suitable for use in power-generating gas turbines, aircraft engines and the like, as well as a method for preparing the same.Thirdly, this invention relates to TiAl intermetallic compound-based alloys having high strength, good creep resistance and good oxidation resistance and hence suitable for use in power-generating gas turbines, aircraft engines and the like.2. Background Art(1) Background art concerning the first class of TiAl intermetallic compound-based alloys in accordance with the present in...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C22C14/00
CPCC22C14/00C22F1/183
Inventor TETSUI, TOSHIMITSU
Owner MITSUBISHI HEAVY IND LTD
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